Patterned, flame resistant fabrics and method for making same

ABSTRACT

The present disclosure relates to patterned, flame resistant fabrics and methods of making them. Generally speaking, the fabrics comprise a plurality of high tenacity, flame resistant fibers, and a plurality of cellulosic fibers containing a flame retardant compound, and at least one color which is printed on the fabric to form the pattern. In a preferred embodiment, the flame resistant fibers are para-aramid fibers and the cellulosic fibers are rayon fibers to yield a strong, flame resistant fabric.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/062,805, filed Apr. 20, 1998, now U.S. Pat. No. 6,132,476,and further claims the benefit of the filing date of U.S. ProvisionalPatent Application Ser. No. 60/149,792, filed Aug. 19, 1999. Both ofthese applications are hereby incorporated by reference into the presentdisclosure.

FIELD OF THE INVENTION

The present invention relates to patterned, flame resistant fabrics.More particularly, the present invention relates to flame resistantfabrics well suited for use in the construction of camouflage battledress uniforms. In addition, the invention relates to methods for makingsuch fabrics.

BACKGROUND OF THE INVENTION

Presently, U.S. infantry troops are issued camouflage patterned garmentsknown as battle dress uniforms (BDUs). BDUs are used both in battle andduring the execution of other tasks associated with military service.The BDUs in current use are either provided with a three or four colorcamouflage pattern that is printed directly onto the surface of thegarment fabric. The nature of the pattern (e.g., color depth), as wellas the particular physical construction of the fabric (e.g. fibertypes), are dictated by to military specifications designated asMIL-C-44436(GL) and MIL-C-44031D. These specifications there developedafter the creation and adoption of a material presently used by themilitary for all BDUs known as “Nyco.” This material comprises 50/50)blend of nylon and cotton. Because the specifications were written basedupon the Nyco material, many of the construction characteristicsidentified in MIL-C-44436(GL) and MIL-C-44031D specifically pertain tothis material.

Although most military personnel are issued BDUs, troops involved inspecialized areas of military service are often provided with flameresistant uniforms. For example, troops that work in close proximity toflammable liquids such as pilots, combat vehicle crewmen, and fuelhandlers are outfitted with garments composed of meta-aramid fibers suchas NOMEX^(R) fibers, which are manufactured by DuPont of Wilmington,Del.

Recently, the federal government has expressed interest in providingflame resistant BDUs to military personnel. Although personnel could beissued BDUs constructed primarily of meta-aramid fibers to obtain thedesired flame resistance, the costs of providing each person with such agarment would be extremely large. In addition, the tensile and tearstrengths of such a fabric would likely fall far short of therequirements of MIL-C-44436(GL) and MIL-C-44031D. Although there areknown fibers that have desirable flame resistance properties as well ashigh tensile and tear strengths, use of such fibers is generally notconsidered viable for BDU construction because it is difficult to formdurable patterns on many of these fibers.

From the above, it can be appreciated that it is desirable to have apatterned, flame resistant fabric which would be a suitable substitutefor existing BDU materials. Furthermore, it should be desirable to havea method for making such a fabric.

SUMMARY OF THE INVENTION

The present disclosure relates to patterned, flame resistant fabrics.Generally speaking, the fabrics comprise a plurality of high tenacity,flame resistant fibers, and a plurality of cellulosic fibers containinga flame retardant compound, and at least one color which is printed onthe fabric to form the pattern. In a preferred embodiment, the flameresistant fibers are para-aramid fibers and the cellulosic fibers arerayon fibers.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure relates to flame resistant fabrics that are wellsuited for use to in the construction of military BDUs. Although thediscussion that follows focuses on BDUs and U.S. military specificationsMIL-C-44436(GL) and MIL-C44031D, it is to be understood that the fabricsdescribed herein could be used in various other applications, ifdesired. In addition, it is to be understood that, for purposes of thepresent disclosure, fibers identified by a named material followed bythe term “fiber” are not limited to fibers composed exclusively of thenamed material.

As identified above, MIL-C-44436(GL) and MIL-C-44031D contain manyphysical property requirements for materials used to construct BDUs. Inview of the aforementioned difficulties in designing a flame resistantBDU, of particular concern is fabric durability as defined by tensile(i.e. breaking) strength and tear strength. Table I provides the class 1requirements set by MIL-C-44436(GL), published Jul. 13, 1992, andMIL-C-44031D, published Dec. 4, 1985, and amended on Sep. 2, 1987, bothof which are hereby incorporated by reference into the presentdisclosure.

TABLE I Summer Weight Winter Weight Fabric Property (MIL-C-44436(GL))(MIL-C-44031D) Breaking strength, (pounds) min. Warp 200 200 Filling 90125 Tearing strength, (pounds) min. Warp 7.0 11 Filling 5.0 8

In an effort to obtain substantial compliance with these strengthrequirements, the fabric of the present invention preferably comprises aplurality of high tenacity, flame resistant fibers. Preferred for thehigh tenacity, flame resistant fibers are non-producer coloredpara-aramid fibers. Such fibers are currently available under thetrademarks KEVLAR^(R), TECHNORA^(R), and TWARON^(R) from DuPont, Teijin,and Acordis, respectively. As is known in the art, para-aramid fibersare composed of aromatic polyamide. Although meta-aramid fibers are alsocomposed of aromatic polyamide, para-aramid fibers are preferred overmeta-aramid fibers because para-aramid fibers are considerably stronger.

To reduce manufacturing costs, improve wearer comfort, and improve theprintability of patterns onto the material, the fabric of the presentinvention further preferably comprises a plurality of cellulosic fibers.Preferred for the choice of cellulosic fibers are rayon, acetate,triacetate, and lyocell. These cellulosics, although softer and lessexpensive than the high tenacity, flame resistant fibers, are notnaturally resistant to flame. To increase the flame resistance of thesefibers, one or more flame retardants are incorporated into the fibersduring the manufacturing process. Effective flame retardants includephosphorus compounds and antimony compounds. Generally speaking,cellulosic fibers which contain one or more flame retardants are giventhe designation “FR” which indicates a flame resistant fiber.Accordingly, the preferred flame resistant cellulosic fibers are FRrayon, FR acetate, FR triacetate, and FR lyocell. Most preferably, theflame resistant cellulosic fibers are FR rayon fibers.

Typically, the blend has a percentage composition of para-aramid fibersof at least 10%, with the balance primarily comprising FR rayon fibers.Preferably, the percentage composition of the para-aramid fibers isbetween 10% and 60%, with approximately 40% being most preferred.Although the current military specifications require a 50/50 blend ofnylon and cotton, the presently preferred blend of para-aramid and FRrayon fibers is believed to be an acceptable substitute in situationswhere thermal and/or flame resistance is desired. Due to thisalternative construction, it will be appreciated that several of thephysical construction requirements (e.g., yarn weight, yarns per inch)identified in MIL-C-44436(GL) and MIL-C-44031D might not be satisfied byfabric constructed in accordance with the present disclosure. However,these differences are deemed to be secondary in importance to providinga strong, flame resistant material.

In addition to the two primary fiber components identified above, thefabric can further comprise approximately 1% to 5% by percentagecomposition of an anti-static fiber. Although the provision of such ananti-static fiber is not considered necessary, it 2( ) may be desirable.When used, the anti-static fiber can comprise a fiber having apolyethylene-carbon core with a nylon sheath such as P140 manufacturedby DuPont, or F7105C manufactured by BASF.

In keeping with MIL-C-4436(GL) and MIL-C-44031D, the fabric of thepresent invention preferably is arranged as a rip-stop for summer weightgarments, and a twill weave for winter weight garments. By way ofexample, the fabric can comprise a plurality of blended yarns havingwarp cotton counts of 38/2 c.c. and fill cotton counts of 30/2 c.c. or15/1 c.c., with the fabric having approximately 96 ends per inch(e.p.i.) and approximately 54 picks per inch (p.p.i.).

Tables II and III provide breaking strength and tearing strength data,respectively, for a prototype summer weight fabric constructed inaccordance with the present disclosure. This fabric comprised a 60/37/3blend of FR rayon, KEVLAR^(R), and anti-static fibers. The blend wasdyed a base shade and printed with four different colors to form thedesired camouflage pattern. Although the breaking strengths identifiedin Table II are not as great as those presently required byMIC-4446(GL), these data suggest that breaking strength values insubstantial compliance with the requirements are achievable.

TABLE II Breaking strength, (pounds) Warp 160 Filling 100

With regard to tearing strength, the prototype fabric exceeded thecurrent requirements of MIL-C-44436(GL) as indicated in Table III.

TABLE III Tearing strength, (pounds) Warp 9.3 Filling 6.9

In addition to achieving substantial compliance with the strengthrequirements of the military specifications, of particular concern issatisfaction of the pattern requirements established for BDUs.Preferably, the camouflage patterns are applied to the BDU fabric byfirst dyeing the fabric a base shade and then dye printing over the baseshade with the other colors of the pattern. As mentioned above, thedifficulty in dyeing (and dye printing), high tenacity, flame resistantfabrics complicates satisfaction of the pattern requirements. Thereasons for this difficulty are the same as those described in relationto fabric dyeing in related U.S. patent application Ser. No. 09/062,805,filed Apr. 20, 1998, now U.S. Pat. No. 6,132,476. As identified in thatapplication, the flame retardants contained in FR cellulosics tend to bedepleted by the relatively high temperatures generally considerednecessary to affix dye within flame resistant fibers such as para-aramidfibers. The depletion of these flame retardants significantly reducesthe flame resistance of the cellulosic fibers and therefore reduces theflame resistance of these blends.

The inventors have discovered that, contrary to conventional beliefs,high tenacity, flame resistant fibers such as para-aramid fibers can bedyed and/or dye printed at temperatures below 100° C. if particulardye-assistants are used during fabric processing. Dyeing and/or dyeprinting at these low temperatures avoids flame retardant depletion. Itis this discovery that has led to the determination that a pattern, suchas a camouflage pattern, can be formed on a flame resistant fabric bydyeing the high tenacity, flame resistant fibers and cellulosic fibers alight base shade at a temperature below 100° C. and then printing theremaining colors of the camouflage pattern onto the blend. Processing inthis manner, a strong, flame resistant BDU can be produced whichsubstantially satisfies the pattern requirements of the militaryspecifications identified above.

The preferred dye-assistants for dyeing the high tenacity, flameresistant fibers of the blend are selected from the group consisting ofN-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide,N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt,N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, arylether, Haco-mid M-8/10 (an approximately 50/50 blend ofN,N-dimethylcaprylamide and N,N-dimethylcapramide), and mixturesthereof. Most preferably, however, the dye-assistant is selected fromthe group consisting of aryl ether, benzyl alcohol, N,N-dibutylformamide, N-octylpyrrolidone, and mixtures thereof.

To accomplish dyeing of the high tenacity, flame resistant fibers of theblend, a dye-assistant, a dye, and other additives if desired, typicallyare applied to the fabric using a one-step batch-type process. By way ofexample, basic, acid, or disperse dyes can be used to dye the hightenacity, flame resistant fibers. In one embodiment, a roll of fabric isloaded into a jet dyer such as a pressure jet dyeing vessel in which thefabric can be circulated through an apertured venturi contained withinthe vessel. The fabric first is scoured and then is dyed with the aid ofthe selected dye-assistant. The temperature of the dyebath normally isincreased gradually from room temperature to a peak temperature belowapproximately 100° C. Preferably, the peak temperature is approximately85° C. Upon reaching the predetermined peak temperature, the dyebathtemperature is maintained to allow dye to penetrate the fibers.

In another embodiment, the fabric is beam dyed in conventional manner.Although jet and beam dyeing are preferred, it is to be understood thatother known atmospheric dyeing methods may be equally advantageous.Irrespective of the particular dyeing method used, there is no need topressurize the dyebath to prevent boiling since the dyeing temperaturedoes not reach or exceed 100° C. Therefore, all dyeing can be conductedat atmospheric pressure. Optionally, the flame resistant cellulosicfibers can be dyed in similar manner. This dyeing can be conducted priorto, simultaneously with, or subsequent to dyeing of the high tenacity,flame resistant fibers. In that the cellulosic fibers normally readilyaccept dye, no dye-assistant is needed to dye the fibers. By way ofexample, direct or reactive dyes can be used to dye the cellulosicfibers.

Once the fabric has been dyed to the desired depth of shade (typically alight green or khaki for camouflage), if at all, the fibric is printedwith conventional methods. By way of example, this printing can beaccomplished with rotary screen printing apparatus. As will beappreciated by persons having ordinary skill in the art, printing can beachieved with dyes, pigments, or a combination of both. Where the fabricis to be dye printed, the aforementioned dye-assistants are useful inpermitting the dye to penetrate the high tenacity, flame resistantfibers. In one embodiment, this dye-assistant can be added to the printpaste. Alternatively, dye printing can be facilitated with dye-assistantcontained within the fibers that has not been removed (e.g., if thefabric is not rinsed before printing). By way of example, basic, acid,or disperse dyes can be used to dye print the high tenacity, flameresistant fibers.

Where both the high tenacity, flame resistant fibers and the cellulosicfibers are to be dye printed, printing of the two fiber types can beaccomplished simultaneously. Where dye printing of the individual hightenacity, flame resistant fibers is not desired or deemed necessary,dye-assistant is not needed. In such a case, the dye-based print pastemay only penetrate the flame resistant cellulosic fibers. Suitable dyesfor these fibers include direct, reactive, and vat dyes. Of these, vatdyes may be preferable in military applications due to their infraredspectral reflectance properties.

When the fabric is to be pigment printed only, dye-assistant isunnecessary in that the pigment is applied to the fabric as a surfacecoating instead of a fiber penetrating dye. Although such pigmentprinting is feasible, it is presently prohibited by the militaryspecifications identified herein and therefore not presently preferred.As mentioned above however, because these specifications may change overtime, an at least partially pigment printed fabric is presentlycontemplated.

Once printed, the fabric then can be finished in a conventional manner.This finishing process can include the application of wicking agents,water repellents, stiffening agents, softeners, and the like. Throughthese techniques, it is believed that full shades of color areachievable which substantially comply with the military BDUspecifications.

While preferred embodiments of the invention have been disclosed indetail in the foregoing description and drawings, it will be understoodby those skilled in the art that variations and modifications thereofcan be made without departing from the scope of the invention as setforth in the following claims.

1. A patterned flame resistant fabric, comprising: a plurality of non-producer colored high tenacity, flame resistant fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant fibers; and at least one color that is printed on the fabric to form said pattern.
 2. The fabric of claim 1, wherein said high tenacity, flame resistant fibers are para-aramid fibers.
 3. The fabric of claim 1, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 4. The fabric of claim 1, wherein said cellulosic fibers are rayon fibers.
 5. The fabric of claim 1, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of at least 10%.
 6. The fabric of claim 1, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60%.
 7. The fabric of claim 1, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of approximately 40%.
 8. The fabric of claim 1, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.
 9. The fabric of claim 1, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 10. The fabric of claim 1, wherein the fabric comprises a plurality of colors that are printed on the fabric to form said pattern.
 11. The fabric of claim 10, wherein said pattern is a camouflage pattern.
 12. The fabric of claim 10, wherein said non-producer colored high tenacity, flame resistant fibers and said cellulosic fibers are dyed a base shade of color.
 13. A camouflaged-patterned flame resistant fabric, comprising: a plurality of non-producer colored para-aramid fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant para-aramid fibers; and a plurality of colors that are printed on the fabric to form a camouflage pattern.
 14. The fabric of claim 13, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 15. The fabric of claim 13, wherein said cellulosic fibers are rayon fibers.
 16. The fabric of claim 1, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60%.
 17. The fabric of claim 13, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 18. The fabric of claim 13, wherein said non-producer colored para-aramid fibers and said cellulosic fibers are dyed a base shade of color.
 19. A patterned flame resistant garment, comprising: fabric that includes: a plurality of non-producer colored high tenacity, flame resistant fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant fibers; and at least one color that is printed on the fabric to form said pattern.
 20. The garment of claim 19, wherein said high-tenacity, flame resistant fibers are para-aramid fibers.
 21. The garment of claim 19, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 22. The garment of claim 19, wherein said cellulosic fibers are rayon fibers.
 23. The garment of claim 19, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of at least 10%.
 24. The garment of claim 19, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60%.
 25. The garment of claim 19, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of approximately 40%.
 26. The garment of claim 19, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.
 27. The garment of claim 19, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 28. The garment of claim 20, wherein the garment is a component of a battle dress uniform (BDU).
 29. A patterned flame resistant fabric, comprising: a plurality of high tenacity, flame resistant fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant fibers; and at least one color that is printed on the fabric to form said pattern.
 30. The fabric of claim 29, wherein said high tenacity, flame resistant fibers are para-aramid fibers.
 31. The fabric of claim 29, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 32. The fabric of claim 29, wherein said cellulosic fibers are rayon fibers.
 33. The fabric of claim 29, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of at least 10%.
 34. The fabric of claim 29, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60 %.
 35. The fabric of claim 29, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of approximately 40%.
 36. The fabric of claim 29, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.
 37. The fabric of claim 29, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 38. The fabric of claim 29, wherein the fabric comprises a plurality of colors that are printed on the fabric to form said pattern.
 39. The fabric of claim 38, wherein said pattern is a camouflage pattern.
 40. The fabric of claim 38, wherein said high tenacity, flame resistant fibers and said cellulosic fibers are dyed a base shade of color.
 41. A camouflaged-patterned flame resistant fabric, comprising: a plurality of para-aramid fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the para-aramid fibers; and a plurality of colors that are printed on the fabric to form a camouflage pattern.
 42. The fabric of claim 41, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 43. The fabric of claim 41, wherein said cellulosic fibers are rayon fibers.
 44. The fabric of claim 29, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60 %.
 45. The fabric of claim 41, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 46. The fabric of claim 41, wherein said para-aramid fibers and said cellulosic fibers are dyed a base shade of color.
 47. A patterned flame resistant garment, comprising: fabric that includes: a plurality of high tenacity, flame resistant fibers; a plurality of cellulosic fibers containing a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant fibers; and at least one color that is printed on the fabric to form said pattern.
 48. The garment of claim 47, wherein said high-tenacity, flame resistant fibers are para-aramid fibers.
 49. The garment of claim 47, wherein said cellulosic fibers are selected from rayon, acetate, triacetate, and lyocell.
 50. The garment of claim 47, wherein said cellulosic fibers are rayon fibers.
 51. The garment of claim 47, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of at least 10%.
 52. The garment of claim 47, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers from approximately 10% to 60 %.
 53. The garment of claim 47, wherein said fabric has a percentage composition of high tenacity, flame resistant fibers of approximately 40%.
 54. The garment of claim 47, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of N-cyclohexylpyrrolidone, benzyl alcohol, N,N-dibutylformamide, N,N-diethylbenzamide, hexadecyltrimethyl ammonium salt, N,N-dimethylbenzamide, N,N-diethyl-m-toluamide, N-octylpyrrolidone, aryl ether, an approximately 50/50 blend of N,N-dimethylcaprylamide and N,N-dimethylcapramide, and mixtures thereof.
 55. The garment of claim 47, wherein said fabric contains a residual amount of a dye-assistant selected from the group consisting of aryl ether, benzyl alcohol, N,N-dibutyl formamide, N-octylpyrrolidone, and mixtures thereof.
 56. The garment of claim 48, wherein the garment is a component of a battle dress uniform (BDU).
 57. A patterned flame resistant fabric comprising: a plurality of high tenacity, flame resistant fibers; a plurality of cellulosic fibers comprising a flame retardant compound, the cellulosic fibers being blended with the high tenacity, flame resistant fibers; and at least one color that is dye printed on the fabric to form the pattern.
 58. A patterned flame resistant garment comprising the fabric of claim
 57. 59. A camouflaged-patterned flame resistant fabric comprising: a plurality of para-aramid fibers; a plurality of cellulosic fibers comprising a flame retardant compound, the cellulosic fibers being blended with the para-aramid fibers; and a plurality of colors that are dye printed on the fabric to form a camouflage pattern. 